Composition for insulating material



UNITED STATES PATENT OFFICE ELIHU THOMSON, OF LYNN, MASSACHUSETTS, ASSIGNOR TO THE THOMSON- HOUSTON ELECTRIC COMPANY, OF CONNECTICUT.

COMPOSITION FOR INSULATING MATERIAL.

SPECIFICATION forming part of Letters Patent No. 460,765, dated October 6, 1891.

Application filed August'fi, 1839- Serial No, 319,827. (No specimens.)

To all whom i may concern: heat, forms the medium for holding the other Be it known that I, ELIHU THOMSON, a citiparticles in place, and gives solidity and body zen of the United States, and a resident of to the whole compound. The proportions Lynn, in the county of, Essex and State of may be varied in accordance with the degree 5 Massachusetts, have invented a certain new of toughness, rigidity,orhardness, or heat-reand useful Composition for Insulating Matesisting qualities required in each case. Thus, rial, of which the following is a specification. when an excellent finish of exterior is de- My present invention relates to a compost sired in the pieces molded from this composition for insulating material which can be tion the proportion of rubber may be in- 1o molded into form, which is to a great extent creased, while the asbestus is diminished. In fire-resisting or heat-resisting, and which has cases where great toughness and fire or heat great strength or toughness so that it can be resisting quality are needed the asbestos or drilled, tapped, or cut, &c., very much in the soapstone are increased in amount, whilethe same manner as a metallic substance. amount of rubber is made as little as possible [5 The substances entering into the composiconsistent with proper holding of the rest of iion of the material are, chiefly, rubber or the materials together. All of the materials similar insulating cementing material, asbesused are insulators. My invention is not retus or similar mineral fiber ground into fine stricted to a composition made of these mapowder or otherwise suitablysnbdivided', and terials alone; but other materials might be 2o soapstone or similar lubricating material added without to any great extent interfersuch, for instance, as tale in fine powder. ing with the properties of the finished pro- These three materials are incorporated in a duct. Thus a moderate proportion of powpowdered ordisintegrated state and molded by dered slate or powdered pumice-stone, rotten heatand great pressureinto the form desired, stone, or other such fine powder might be 25 themixture being verycomplete and perfectly added, provided the amount is not suificient made. The rubber used may be scrap vulto overcome the lubricating quality of the canized rubber or maybe any form of rubber soapstone or talc powder which has been or other material in its natural state, or which introduced into the composition for the purhas been vulcanized in part or completely, pose above mentioned. Other binding mate- 8o 0 and which is subject to hardening by conrials of a similar nature to asbestus may be tinned heat under pressure, as in the ordinary substituted to give toughness-such as minvulcanizing or rubber-working processes. It eral wool, fine -sp un glass, &cwhile again pure rubber be useda suitable amount of vulthe rubber in the composition may be either canizing material is added with it. A large pure rubber or an impure mixture, or there proportion of asbestos fiber or other similar may be substituted for it other materials fiber of a mineral nature and incombustible, which soften by heat and yield under pressand which is also heat non-conducting and ure or become plastic under pressure, as does electrically a perfect insulator, is preferably the rubber, while it is at all times a high inemployed. The soapstone reduced to a fine sula'tor capable offilling the pores of the 40 state of division before mixing with the other asbestus and soapstone and capable of being materials, which have also been put into with the other materials rendered slightly shape for complete admixture, acts as a luyielding or elastic when hot, and assuming brieant, allowing the material to flow under its rigidity or toughened form when cold. pressure. It also gives body to the material Evena strong solution of rubber, as asolvent, 45 and adds its fire-proof qualities, and at the might be incorporated with the other subsame time asststs in allowing tapping or cutstances and allowed to dry out, so as to leave ting of the material into shape. The asbesthe rubber in thorough admixture with the tus, being a fire-proof and fibrous material, restofthe materials before molding and press confers toughness. The rubber is the binding into shape. :00 5o ing material, which, when vulcanized or hard- A quantity of the completed material may ened and consolidated by great pressure and be introduced in a heated state into a mold and assume a rigid, tough fer-uncut: side.

My invention therefore consists in a combination of at least three materials having opposing properties and all insulators electrically, to wit, one a lubricant insulator, as talc or soapstone, another a fibrous material insulator capable of resisting heat, such as asbestus,.and the third a material of good insu'lating quality, becoming plastic under high temperatures and solidifying again when cold, and capable of admixture with the former materials as well as possessed of a good degree of toughness of itself while not being easily softened by heat or set on fire.

On account of its expense it is well to reduce the proportion of rubber to the greatest degree practicable and retain the requisite strength. 3 This proportion may vary from fifteen per cent. to twenty-five per cent., according to the coherence desired in the material, my preference being for about twentyfive per cent, and the proportion of asbestus and soapstone added may be such as will suit the conditions of toughness and rigidity; but

in all cases enough soapstone-say five to fifteen per cent.must be added to allow the material to flow slightly and be plastic in the molds, so as to conform readily to the shape of the molds. As I have stated above, these materials may have added to them other practically inert materials used merely as a filling, the chief properties being conferred by the materials which I have mentioned as constituting the combination of my invention. It is also Well to coat the molds with the lubricating material, such as soapstone, before introducing the material to be molded.

What I claim as my invention is 1. An electrical insulating composition consisting of a fibrous. unnfial'ihwtggasa base, a cementing insulating substa ncansuch as rubber, and a lubricawijpgi stingpf an insulating materialfas and for the purpose described.

2. A composition for an electrical insulating material, consisting of -asbes-tus, .rub ber,

and soapstone, or.theirinsulating equivalents,

as described, combined in the manner and for the purposes set forth.

Signed at Lynn, in the county of Essex and State of Massachusetts, this 1st day of August, A. D. 1889.

ELIHU THOMSON.

Witnesses J OHN W. GIBBONEY, A. L. ROHRER. 

